# gleamtk

Proof of concept: a **Relm4** (GTK4 / libadwaita) process that acts as an
**Erlang foreign node**, controlled by a **Gleam** process over the Erlang
distribution protocol.

```
Gleam (beam)  ── cookie + epmd ──►  Relm4 foreign node (Rust)
gleamtk@127.0.0.1                   ui@127.0.0.1
  controller  ── {gui, Node} ! ──►  registered name: gui
  ◄── events ── {controller, …} ──  clicks / ready / pong
```

## Protocol

**Gleam → UI** (`{gui, 'ui@127.0.0.1'} ! Term`):

| Term | Effect |
|------|--------|
| `hello` | Handshake; UI records controller pid |
| `{set_title, Binary}` | Window title |
| `{set_label, Binary}` | Main label |
| `{set_count, Int}` | Counter display |
| `ping` | UI replies `pong` |

**UI → Gleam** (to registered `controller` or the sender pid):

| Term | Meaning |
|------|---------|
| `{ready, <<"ui@…">>}` | UI node is up |
| `{clicked, Count}` | Primary button |
| `{count_changed, Count}` | − button |
| `pong` | Reply to `ping` |
| `window_closed` | Window closed |

## Requirements

- Nix (recommended) or: Erlang/OTP, Gleam, Rust, GTK4, libadwaita, epmd
- A display (Wayland/X11) for the Relm4 window

## Run

```bash
cd gleamtk
nix develop          # or: nix develop -c bash
just run             # starts UI then Gleam controller
```

Two terminals:

```bash
# terminal 1
just ui

# terminal 2
just gleam
```

Click **Click me** / **+** in the window. Gleam prints events and updates the
label and count over distribution.

## Layout

```
gleamtk/
  gleam/           # Gleam controller (BEAM node)
  ui/              # Relm4 + erl_dist foreign node
  justfile
  flake.nix
```

## Notes

- Cookie defaults to `gleamtk`; both sides must match.
- Long node names on `127.0.0.1` avoid short-name / hostname mismatches.
- The Rust side uses [`erl_dist`](https://crates.io/crates/erl_dist); the UI
  thread never blocks on distribution I/O.
- This is a POC, not a full widget toolkit binding.